1. Field of the Invention
The present invention relates to a zoom lens system, and more particularly, to an inner-focus type zoom lens system for use in an image-pickup camera module having an image sensor therein.
2. Description of the Related Art
In a focusing system of a zoom lens, a front-focus type system for moving a first lens group closest to an object side is generally used. Since a movement amount of the first lens group required for focusing an object located at the same distance does not depend on a focal length of a lens in the front-focus type system, the front-focus type system is widely used.
However, since the front-focus type system moves the first lens group, which is relatively big and heavy, to perform focusing, the front-focus type system has a disadvantage that a focusing speed is slow and much driving power is required. Further, since a plurality of lenses are used so as to obtain excellent optical characteristics such as high resolution, a camera module has a large size and difficult to mount on a portable apparatus.
For another focusing system of a zoom lens, there is a rear-focus type system moving a lens located at an image-surface side. The rear-focus type system has a problem that a movement amount of a focusing lens required for focusing an object located at the same distance is varied depending on a zooming position (i.e., the focal length of the lens) and that a focus is lost when zooming is performed after focusing is once performed for a close distant object.
For another focusing system of a zoom lens, there is an inner-focus type system moving a lens located between an objective lens and a condensing lens.
The above focus type systems move one or more lens groups so as to perform zooming and move another lens group so as to correct an image plane formed by the moving of the lens group, so that a lens moving apparatus is complicated and is difficult to manufacture in a small size.
Therefore, a zoom lens system capable of achieving a sufficient zooming performance and high resolution by moving only one lens group, is highly required.